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Short-term response of Arctic vegetation NDVI to temperature anomalies / I. Olthof in International Journal of Remote Sensing IJRS, vol 28 n° 21-22 (November 2007)  

Public [article]  inInternational Journal of Remote Sensing IJRS > vol 28 n° 21-22 (November 2007) . - pp 4823 - 4840 Titre : Short-term response of Arctic vegetation NDVI to temperature anomalies Type de document : Article/Communication Auteurs : I. Olthof, Auteur ; R. Latifovic, Auteur Année de publication : 2007 Article en page(s) : pp 4823 - 4840 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement d'image [Termes IGN] anomalie thermique [Termes IGN] Arctique [Termes IGN] Canada [Termes IGN] changement climatique [Termes IGN] détection de changement [Termes IGN] Normalized Difference Vegetation Index [Termes IGN] surveillance de la végétation Résumé : (Auteur) The effects of climate change on northern vegetation productivity need to be fully understood in order to reduce uncertainties in predicting vegetation distributions under different climate warming scenarios. Knowledge of the relationship between northern climate and vegetation productivity will also help provide a better understanding of changes in vegetation distributions as an indicator of climate change and variability. Vegetation productivity and biomass have been monitored using long-term satellite earth observations, mostly using the Normalized Difference Vegetation Index (NDVI), as a cumulative indicator of all effects resulting from processes related to climate change, including changes in temperature, precipitation, and disturbance. In this paper, the investigation is focused on the short-term effect of temperature anomalies on arctic and tree-line transition vegetation productivity in both dry and humid regions of Canada. The analysis shows that several land-cover types composed mainly of trees and shrubs exhibit a significant increase in NDVI with higher-than-normal temperatures in the preceding 10-40-day period, while land-cover types consisting of lichen and moss growing on mostly barren surfaces show a significant NDVI decrease with increased temperature. These trends are consistent with results reported in plot-warming experiments in the north, which have shown that certain vegetation communities increase, while others decrease in cover fraction and biomass in response to warming. When land cover is grouped into increasing and decreasing NDVI with temperature and stratified by dry and humid regions of Canada, much of the dry region of northern Canada does not exhibit significant NDVI response to preceding temperature anomalies. It is expected that in the absence of disturbance or other limiting factors, an increased frequency of elevated temperature anomalies may eventually contribute to changes in vegetation biomass. A map of land-cover types that have the potential to increase in biomass with climate warming and those that are vulnerable to decline is presented. Copyright Taylor & Francis Numéro de notice : A2007-491 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1080/01431160701268996 En ligne : https://doi.org/10.1080/01431160701268996 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=28854 [article]

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Landsat-7 ETM+ radiometric normalization comparison for northern mapping application / I. Olthof in Remote sensing of environment, vol 95 n° 3 (15/04/2005)  

Public [article]  inRemote sensing of environment > vol 95 n° 3 (15/04/2005) . - pp 388 - 398 Titre : Landsat-7 ETM+ radiometric normalization comparison for northern mapping application Type de document : Article/Communication Auteurs : I. Olthof, Auteur ; D. Pouliot, Auteur ; R. Fernandes, Auteur ; R. Latifovic, Auteur Année de publication : 2005 Article en page(s) : pp 388 - 398 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement d'image optique [Termes IGN] analyse comparative [Termes IGN] cartographie numérique [Termes IGN] correction radiométrique [Termes IGN] image Landsat-ETM+ [Termes IGN] image SPOT-Végétation [Termes IGN] méthode robuste [Termes IGN] mosaïque d'images [Termes IGN] propagation d'erreur [Termes IGN] régression Résumé : (Auteur) Relative radiometric normalization has long been performed to generate consistency among individual Landsat scenes for production of composites containing multiple scenes. Normalization methods have relied on matching identical and assumed invariant features in both images of an overlapping pair, or on invariant targets that are not necessarily the same features. Problems with overlap normalization methods include sensitivity to outliers in overlap data caused by atmospheric or land cover change between scenes, which can lead to radiometric error propagation across a mosaic caused by a normalized scene becoming a reference for the subsequent scene entered into the mosaic. Solutions to such problems include interactive outlier removal to generate a normalization function using a 'no change' data set and methods that are robust against outliers to automatically generate normalization functions with minimal user input. This paper compares two normalization methods that use a robust regression technique called Theil-Sen with an established overlap normalization method. The first method uses Theil-Sen regression to generate a normalization function between overlap regions, while the second uses Theil-Sen to normalize to coarse-resolution composite reflectance data from the SPOT VEGETATION (VGT) sensor. The results of the normalizations were evaluated in two ways: (1) using statistics generated between overlap regions; and (2) separately using coarse-resolution data as a reference. Both overlap normalization methods performed almost identically; however, Theil-Sen was faster and easier to implement than its traditional counterpart due to its insensitivity to outliers and capability for full automation. While overlap and coarse-resolution normalizations each outperformed the other when evaluated against its calibration set, error propagation caused by outliers in overlap samples was avoided in the normalization to coarse-resolution imagery. Advantages offered by normalization to coarse-resolution data using robust regression, including full automation, make this method particularly attractive for generation of large area mosaics containing 100 Landsat scenes or more. Numéro de notice : A2005-171 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/j.rse.2004.06.024 En ligne : https://doi.org/10.1016/j.rse.2004.06.024 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=27309 [article]

Signature extension through space for northern landcover classification: a comparison of radiometric correction methods / I. Olthof in Remote sensing of environment, vol 95 n° 3 (15/04/2005)  

Public [article]  inRemote sensing of environment > vol 95 n° 3 (15/04/2005) . - pp 290 - 302 Titre : Signature extension through space for northern landcover classification: a comparison of radiometric correction methods Type de document : Article/Communication Auteurs : I. Olthof, Auteur ; C. Butson, Auteur ; R. Fraser, Auteur Année de publication : 2005 Article en page(s) : pp 290 - 302 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement d'image optique [Termes IGN] agriculture [Termes IGN] analyse comparative [Termes IGN] classificateur paramétrique [Termes IGN] correction radiométrique [Termes IGN] image Landsat [Termes IGN] limite de résolution géométrique [Termes IGN] occupation du sol [Termes IGN] phénologie [Termes IGN] prévision [Termes IGN] signature spectrale Résumé : (Auteur) Northern landcover mapping for climate change and carbon modeling requires greater detail than what is available from coarse resolution data. Mapping landcover with medium resolution data from Landsat presents challenges due to differences in time and space between scene acquisitions required for full coverage. These differences cause landcover signatures to vary due to haze, solar geometry and phenology, among other factors. One way to circumvent this problem is to have an image interpreter classify each scene independently, however, this is not an optimal solution in the north due to a lack of spatially extensive reference data and resources required to label scenes individually. Another possible approach is to stabilize signatures in space and time so that they may be extracted from one scene and extended to others, thereby reducing the amount of reference data and user input required for mapping large areas. A radiometric normalization approach was developed that exploits the high temporal frequency with which coarse resolution data are acquired and the high spatial frequency of medium resolution data. The current paper compares this radiometric correction methodology with an established absolute calibration methodology for signature extension for landcover classification and explores factors that affect extension performance to recommend how and when signature extension can be applied. Overall, the new normalization method produced better extension and classification results than absolute calibration. Results also showed that extension performance was affected more by geographical distance than by differences in anniversary dates between acquisitions for the range of data examined. Geographical distance in the north-south direction leads to poorer extension performance than distance in the cast west direction due in part to differences in vegetation composition assigned the same class label in the latitudinal direction. While extension performance was somewhat variable and in some cases did not produce a best classification result by itself, it provided an initial best guess of landcover that can subsequently be refined by an expert image interpreter. Numéro de notice : A2005-170 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/j.rse.2004.12.015 En ligne : https://doi.org/10.1016/j.rse.2004.12.015 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=27308 [article]